1. Field of the Invention
This invention relates generally to an improved twist tie feed device which can be used for tying a group or bundle of items, for example, celery, asparagus, broccoli and the like, and more particularly to an improved twist tie feed device utilizing an electric and pneumatic hybrid drive system.
2. Description of Related Art
Prior art patents teach the development of machines which effectively apply a tie wire about products to protect those products in transit prior to retail sale. The tie is a generally malleable wire sandwiched between two strips of paper secured together, for example with adhesive, to form a generally flat ribbon. The ribbon may also consist of plastic ribbon having a narrow center stripe of greater height than the adjoining areas. After a snug loop of ribbon is formed around the product, the ends of the ribbon are clamped. These clamped ends are then rotated about a central axis producing a permanent twist in the tie ribbon whereby the loop and product are held together. In the known manner, the ribbon can be untwisted by the purchaser of the product and retwisted when it is desired to re-apply the ribbon. These procedures have become most familiar to consumers, with twist ties being used on many products, not only to hold the above mentioned products together, but to provide closure for paper and plastic bags containing foodstuffs and other items and in larger sized bags used for containing potatoes, onions, etc.
Many operational steps are required to apply a twist tie in the form of a wire/paper ribbon. In the past, complex machinery has been designed to effect performance. These machines as illustrated for example, in U.S. Pat. No. 3,318,230 issued May 9, 1967; U.S. Pat. No. 3,428,096 issued Feb. 18, 1969; U.S. Pat. No. 3,898,924 issued Aug. 12, 1975 and U.S. Pat. No. 4,177,842 issued Dec. 11, 1979, each of which are hereby incorporated by reference, are machine constructions relying on complex mechanisms, electrically driven in some instances, and generally using cam devices to provide sequential motions necessary to effect the procedural steps in applying a twist tie ribbon to the product. Each progressive patent generally teaches an improvement in performance and simplification in structure. However, endless belt chain drives, pulleys, and complicated linkage systems are not uncommon, and the need for adjustment for operation and to compensate for temperature variation and for wear can be relatively frequent. Use of both a forward feed drive for the ribbon and also an independent reverse feed drive for tightening the ribbon about the bundle is also disclosed in the prior art, further adding to the complexity of such prior art systems.
It is also known from U.S. Pat. No. 4,559,977 issued on Dec. 24, 1985, which is hereby incorporated by reference, to provide a pneumatic twist tie feed device for providing a helical wrap about the package. This device utilizes a first gripper which clamps and retains the free end of the ribbon against a second gripper. Pressure rollers operate in reverse retracting excess ribbon about the produce. A friction clutch, operative only for reverse ribbon feeding, allows for ribbon slippage as the ribbon tightens around the produce. Then the second gripper clamps the other end of the ribbon against the twister head and a twister mechanism rotates the clamped ends of the ribbon about a common axis twisting the ribbon ends together. Axial gripping motion is provided by cylindrical valves having pistons concentric with and supported by a gripper support rod tube and acting, respectively at the ends of the gripper supports away from the tie ribbon. A rack and pinion mechanism is used to provide rotation of twister mechanism and forward and reverse feeding of the ribbon. All components are pneumatically driven.
While this prior art device has been somewhat satisfactory for its intended purpose, it has also proven to be overly complex for many applications, requiring the simultaneous control of several pneumatic valves and solenoids. Additionally, because the ring was a helical ring, if the helical wrap became shifted to be perpendicular to the bundle, the wrap became loose. Additionally, only a single forward drive wheel was utilized in conjunction with an idler so that during reverse driving, the idler had to be removed from contact with the ribbon, while an accumulator rod was utilized to pull and tension the ribbon in a backward feeding direction.
U.S. Pat. No. 5,121,682 issued on Jun. 16, 1992 to Parker et al., which is hereby incorporated by reference, teaches an improvement on the prior art devices by providing an electric twist tie feed device with a circular wrap, positive drive rollers and a sensor. The positive drive rollers contact the ribbon on either side and feed the ribbon to the circular wrap, moving in the opposite direction to retract any excess ribbon from the ring. A sensor determines when to stop retracting the ribbon to prevent damage to the product being tied.
Although satisfactory, this device uses numerous clutches and brakes, which typically need to be periodically gapped and periodically require the use of lubricants, which can result in lost torque and other problems. Additionally, the parts can wear out, making it difficult to maintain torque.
Accordingly, a need exists for a twist tying machine which is simple and reliable in construction, and reduces the total number of parts, which can provide a circular wrap and may perform wrapping without the use of an accumulator or clutches and brakes.